Project Summary As a result of recent breakthroughs in commercial laser technology, we are requesting a femtosecond pulsed laser source for 3-photon excitation and ultra-deep in vivo imaging. This laser will be integrated into a custom-built microscope that is equipped with adaptive optics and made available to researchers at UT Southwestern Medical Center as part of a new initiative to increase access to advanced imaging technologies. To our knowledge, no 3-photon microscope is publicly available in the United States. Acquisition of the laser will immediately benefit 5 NIH supported laboratories at UT Southwestern, with applications including in vivo imaging of cancer niches and neuronal circuitry.